1. Field of the Invention
This invention relates to a static random access memory (hereinafter referred to as SRAM), and more particularly to an SRAM having a flash-clear function. Description of the Prior Art
Some conventional SRAMs have a flash-clear function. When an SRAM has a flash-clear function, a data "0" is written into all of the memory cells of the SRAM at the same time when a control signal is applied to the SRAM from the outside. The flash-clear function is used to reset an SRAM or make initialization of an SRAM in preparation for testing.
FIG. 5 is a block diagram showing an exemplary SRAM having a flash-clear function. Referring to FIG. 5, the SRAM shown includes a memory cell array a and a flash-clearing decoder b. If a flash-clear control signal is received at the flash-clearing decoder b of the SRAM from the outside, a flash-clearing pull-down transistor (not shown) provided in the memory cell array a is driven to change the voltage level of one of the bit lines of each pair of bit lines B and B to the ground level. With the conventional SRAM shown in FIG. 5, flash-clearing is conducted all at once for the entire memory cell array a by way of the single decoder b.
The SRAM shown in FIG. 5 has the drawback that, since it includes only the one decoder b and flash-clearing is conducted all at once for the entire memory cell array a by way of the single decoder b, the magnitude of the electric current flow through the memory cell array and the decoder upon flash-clearing exhibits a very high peak value as seen in FIG. 6.
Since the storage capacity of such memory devices has increased remarkably in recent years and memory cell arrays are likely to increase in scale, if a large scale memory cell array is flash-cleared in the above described manner, then the current peak will be very high. Where the peak of current is high, naturally the level of the power supply line or the ground line will fluctuate so that electrical signal noises are produced. There is also the possibility that the wires in such a large scale chip may be melted to cause destruction of the internal structure of the chip or cause destruction of an appliance in which the memory device is used. Accordingly, such an excessively high peak current flow upon flash-clearing is an unignorable problem.